Co-pending patent application Ser. No. 10/789,899, titled Mixed Hydrogen Generation Material, and filed Feb. 27, 2004 describes a family of new materials for the storage of hydrogen and methods of making such materials. The materials are characterized by the formula M′xM″yNzHd in which (a) M′ is a cation selected from the group consisting of Li, Ca, Na, Mg, K, Be, and mixtures thereof, and x is in the range from about 50 to about 53; M″ comprises one or more cations selected from Group 13 elements of the Periodic Table (IUPAC notation), and y is in the range from about 5 to about 34; (c) N is nitrogen and z is in the range from about 16 to about 45; (d) H is hydrogen and d is in the range from about 110 to about 177; and (e) M′, M″, x, y, and z are selected to maintain electroneutrality.
The disclosed family of hydrogen storage materials includes a new quaternary hydrogen-rich compound (or mixture) that is made by chemically combining two mole parts of lithium amide (LiNH2) with one mole part of lithium borohydride (LiBH4). This product has a composition close to Li50B17N33H133 and will be referred by this formula throughout this specification. It contains a compound whose composition has been tentatively identified to be approximately Li3BN2H8. Thus, hydrogen is a significant atomic component of each of the precursor compounds and it is retained in the quaternary product molecule as about 11.9 weight percent of the material. Li50B17N33H133 melts at about 190° C. and releases much of its hydrogen (more than 10 wt % of the hydride) when progressively heated in a suitable chamber to about 350° C. After the hydride particles are added to the chamber it may be initially evacuated, or an inert gas or hydrogen may be flowed through the chamber. Thus, this material and its family members offer convenient compounds in which to store releasable hydrogen, particularly for mobile power requirements.
The above identified patent application is incorporated herein by reference for its disclosure of the family of hydrogen storage materials and their preparation and properties. Moreover, a related publication by the inventors herein, “Hydrogen Desorption Exceeding Ten Weight Percent from the New Quaternary Hydride Li3BN2H8” in The Journal of Physical Chemistry B, 2005, 109, pages 6-8 is incorporated into this specification by reference. This publication also describes syntheses of Li50B17N33H133 (in terms of its equivalent nominal formula, Li3BN2H8) and the removal of hydrogen from the quaternary compound by heating to temperatures above about 250° C. This release temperature is undesirably high for mobile applications of hydrogen power.
There remains a need to reduce the temperature of release of hydrogen from these new hydrogen storage materials, preferably below the melting point of the materials, and to increase the rate of release of the hydrogen gas. It is an object of this invention to provide certain additives that enhance the release of hydrogen from the stated family of hydrogen-rich compounds.